Additive Manufacturing (AM) is an emerging part production technology that offers many advantages such as high degree of customization, material savings and design of 3D highly complex structures. However, AM is a complex multiphysics process. Therefore, only a limited number of materials can already be commercially used to produce parts and a handful of others are being studied or developed for such process. Consequently, limited knowledge on this process is available, especially concerning materials that present thermomechanical challenges such as brittle materials.
The research I did during my PhD studies focuses on additive fabrication of silicon pillars on a monocrystalline silicon wafer by Direct Laser Melting (DLM) with a pulsed 1064 nm laser beam. The simple geometry of pillars allowed for the first determining steps into process understanding. Several results were achieved through this PhD work. First, crack-free silicon pillars were successfully built onto monocrystalline silicon wafers. With the help of in-situ process monitoring and sample characterization, wafer substrate temperature and laser repetition rate were found to be the main influential parameters to obtain crack-free samples, as minimum substrate temperature of 730°C and a minimum repetition rate of 100 Hz were necessary to reach this goal (for a feed rate of 15 g/min and a pulse duration of 1 ms). The influence of secondary process parameters such as feed rate and energy per pulse were also discussed. A simple Finite Element Modeling (FEM) model validated by the experiments was used to explain crack propagation in the samples. Then, process monitoring of the DLM process was realized. High-speed camera image analysis revealed that vertical stage speed and powder feed rate should match to obtain a constant pillar building rate. As all pillars presented necking at their base, estimations of the thermal characteristics of the pillar during growth were carried out by FEM simulations. They were more used to explain the pillar final shape. Finally, the microstructure of the pillars built was characterized by the Electron Back-Scattering Dif-fraction (EBSD) technique. In the conditions presented in this work, the microstructure of the pillar was found to be in the columnar growth mode. The feed rate was identified as the most influential parameter on the microstructure, followed by the stage speed, the impurity content of the powder and the crystallographic orientation of the substrate. Epitaxial growth was achieved on more than 1 mm with a feed rate of 1.0 g/min, a stage speed of 0.1 mm/s, a powder with purity of 4N and a <111> oriented wafer substrate. This work could be further continued by making improvements to the DLM setup, studying the influence of additional process parameters on the thermomechanical behavior and the microstructure control of the pillars, and/or using these results to realize more complicated shapes, either with this setup or by using a powder bed technique.
About
I was born in France and I have grown up in a little town called Beynes, in the department Yvelines, no so far from Paris and Versailles. I am the first of four kids! As a child, I wanted to be a journalist. I have always been interested in digging up into a subject in order to transforming into articles that could be read by others. I had a few friends writing a bunch of articles alongside so we could turn everything into magazines. I spent a lot of time playing with a - now old - layout software in order to make this publication look like my favorite magazines at that time – L'Hebdo, le monde des ados. I even managed to get an internship for a week there!
About
I was born in France and I have grown up in a little town called Beynes, in the department Yvelines, no so far from Paris and Versailles. I am the first of four kids! As a child, I wanted to be a journalist. I have always been interested in digging up into a subject in order to transforming into articles that could be read by others. I had a few friends writing a bunch of articles alongside so we could turn everything into magazines. I spent a lot of time playing with a - now old - layout software in order to make this publication look like my favorite magazines at that time – L'Hebdo, le monde des ados. I even managed to get an internship for a week there!
"Chill", my first collection of unique illustrated textile prints
My textile patterns are created from my illustrations and introduce you to nature curiosities
Discover this season's exclusive patterns and the stories behind them, and find the long-sleeved tops, postcards and T-shirts in the online store.
Antarctic volcanoes
Scottish geologists discovered some years ago that 91 volcanoes hide under the ice in Antarctica, making this territory one of the largest volcanic regions in the world. The volcanoes are between 100 and 3850 m high, approaching the altitude of the Eiger, the legendary Swiss summit! If these volcanoes were to erupt, this could have consequences on the melting of the ice, already accelerated by climate change. The problem is that the more it melts, the more likely they are to erupt…
To make this print, I mixed blue and red watercolor tones, letting them intertwine with the water, like lava and ice! I then scanned them and arranged them to form this pattern!
Ice Age
This print pays tribute to some animals of the Megafauna of the last ice age, which disappeared around 13000 years ago. We aren't able to see them in real life (okay, some were probably really scary!), so here is a small cocktail of some of them gathered on this print: the saber-toothed tiger, the mammoth, the megaloceros, the woolly rhinoceros and elements of Dasypus Bellus. Several hypotheses explain the disappearance of these giant mammals. For some, climate change could be responsible. The woolly rhinoceros, for example, would not have known how to adapt to warmer temperatures, nor migrate to a habitat more favorable to its survival. Human migration to more and more ecosystems is a more popular theory to explain their disappearance. The mammoth, for example, was widely hunted by humans. So, human victims or climate change? Both maybe? While theories are jostling, History gives our current era a deja vu atmosphere...
To create this print, I first sketched some of the animals on paper before drawing them on the computer to arrange them into a pattern.
Abyss
Discover some species that live in the abysses, deep in the oceans. The brittle star, a relative of the starfish family, is included in this print. Some species of these echinoderms have been observed down to 8000 m depth! You can also find a Rhinochimaera Atlantica, with its nose that allows it to locate the small fish it feeds on. It can live up to 2000 m deep. The tripod fish is almost blind (not that you can see anything up to 6000 m deep!), but its long fins allow it to land on the ocean floor and feel the vibrations created by the presence creatures crawling through the muddy sediments. Finally, the Dumbo octopus, the cutest of the oceans, can live up to 7000 m deep!
To create this pattern, I first drew each element with a watercolor graphite pencil. I then scanned them to be able to work on the composition of the print on the computer.
The States of Water
Did you know that water is one of the rare compounds to take up more space in solid form than in liquid form? I'm sure you've tried to chill a bottle of water in the freezer, forgotten about it, and then found it exploded hours later! Indeed, the water molecule, made up of one oxygen atom and two hydrogen atoms, is polarized: its oxygen atom attracts the only electrons from its hydrogen atoms. This oxygen atom is then charged negatively and its hydrogen atoms, positively. A hydrogen bond can then form by attraction between the oxygen atom of a water molecule and a hydrogen atom of a neighboring molecule. This bond is less strong than an atomic bond, but is not negligible. Below 0°C, the water molecules arrange themselves in hexagons to take into account these hydrogen bonds, which does not optimize the arrangement of the molecules in the structure of the ice. It takes up more space! This print is inspired by the molecular structures of water in each of its states: solid, liquid and gaseous.
I created this printout on the computer, using images of the molecular structure of ice. After trying several color combinations, I opted for blue, the only color capable of crossing miles of water.
Bat Calls
Although their sight is acceptable, bats use echolocation to better “perceive” their environment, especially when it is dark. They "shout" ultrasounds - often imperceptible to the human ear - which reverberate off the obstacles or the insects they hunt, before returning to them in the form of echoes which bring back information on the size, shape of the object and the distance from it. They use higher frequencies to hunt or detect smaller things, such as insects. This print wants to represent this phenomenon, with the appearance here and there of architectural elements that appear and disappear in the night, as the bats' ultrasounds reveal them.
I painted the design in watercolor on a continuum of four panels of A3 sheets. I then scanned the design and worked it on the computer to make a continuous pattern.
Cryo-genius!
The wood frog, or Rana sylvatica, lives mainly in the forests of the northern USA and Canada. This frog has the particularity of letting its vital functions almost completely freeze in winter. She becomes clinically dead! But thanks to a system of accumulation of urea in its tissues and production of glucose by its liver, among other things, the degradation of its cells is avoided. It can thus survive temperatures down to -18°C!
To create this print, I first individually painted each frog in its ice cube on paper with blue ink. I then scanned my drawings and arranged them on the computer to create the final pattern.
